Lady Gaga has been suffering from food poisoning and altitude sickness during her tour of South America, and she is also wracked with worry as both of her grandparents battle ill health in hospital.

The pop superstar is currently touring the continent with her Born This Way Ball shows but she is missing home and reached out to fans in an emotional post on her website.

Gaga reveals she has been struck down with food poisoning and altitude sickness this week (beg05Nov12), and she is also deeply concerned for her grandparents, who have been hospitalised at home.

The star goes on to complain she will be away from her family during the upcoming Thanksgiving holiday, but she credits her fans with keeping her going through the tough times.

In a post on her LittleMonsters.com page, she writes, "I had food poisoning last night, and now altitude sickness cuz (because) were (sic) 8,000 feet above sea. My grandma AND my grandfather are both in the hospital and I can't see my family for Thanksgiving, and all I can think of is how I want to be a superstar for (the gig in) Columbia (sic)... The only thing keeping me going today is how beautiful Bogota is, I always dreamed of coming here. Thank you monsters (fans) for being my home away from home."